If you use class diagrams to show the "truth" you are in painland in my experience. However I sometimes find them useful to extract key parts of the system and

If you use class diagrams to show the "truth" you are in painland in my experience. However I sometimes find them useful to extract key parts of the system and showing their interaction. Cutting away many attributes, many helper classes, many other things. That can lead to pictures which are quick to grasp and then allow further digging based on code.